There are methods known in the art for producing gasoline from synthesis gas such as the method disclosed in U.S. Pat. No. 3,894,102, however there is a need for improvement in the productivity, heat transfer, reactor size and other significant parameters which can lead to cost efficiency. One of the disadvantages of the process of U.S. Pat. No. 3,894,102 is that it is economically justified only if the syngas feed stock is hydrogen-rich. A more versatile process is desirable. Furthermore, in the prior art process, in the first stage of conversion of the syngas to methanol, a significant amount of water is produced which must be separated from the mixture prior to proceeding to the gasoline synthesis stage.
Other processes related to syngas-to-gasoline conversion include U.S. Pat. No. 4,882,360 describing a process for producing an alcohol fraction comprising methanol, ethanol and some propanol from a syngas using a catalyst consisting of three components: molybdenum sulfide, iron sulfide and a suitable promoter. This does not appear to be a process wherein syngas is made to produce dimethyl ether which is in turn converted to gasoline.
U.S. Pat. No. 4,826,662 discloses an apparatus for reducing the amount of water in the feed to a methanol-to-gasoline reactor. In the first step, methanol is converted to an equilibrium mixture of dimethyl ether, water and methanol and the patent is directed to the reduction of the amount of water in this mixture. Since the presence of water in a gasoline reactor is detrimental in that it deactivates the catalysts irreversibly and limits the maximum temperature at which the reactor can operate due to the amount of steam produced in the reactor effluent, the patent provides a set of primary and secondary distillation towers to dewater the feed. According to the present invention the feed stock is a syngas which produces directly dimethyl ether in a one-step synthesis which obviates the need for dewatering according to this patent.
U.S. Pat. No. 4,814,536 discloses an improvement on the process of converting methanol to gasoline by selectively programming a feed weight hourly space velocity (WHSV) to a fixed bed catalytic conversion reactor so as to increase cycle average gasoline yield and increase useful life in the conversion catalyst.
U.S. Pat. No. 4,898,717 discloses a multistage process for converting C.sub.1 -C.sub.4 aliphatic oxygenares to heavy hydrocarbons in the diesel fuel boiling range. In the first stage the feed is converted to lower olefins and in the second stage the ethane-free lower olefins are converted to diesel fuel boiling range hydrocarbons.
U.S. Pat. No. 4,808,764 describes a method for feeding vaporized methanol into a gasoline reactor in contact with a recycled gas stream as a diluent. By using a proper dilution ratio, the exothermic heat of reaction and adiabatic temperature rise in the gasoline reactor are controlled within tolerable limits for the zeolite catalyst.
U.S. Pat. Nos. 4,788,369 and 4,788,042 are directed to gasoline conversion systems where a light hydrocarbon diluent is recycled.
U.S. Pat. No. 4,606,580 is directed a two-stage Fischer-Tropsch synthesis for the production of diesel and gasoline hydrocarbons from syngas.
U.S. Pat. Nos. 5,524,227 and 5,524,228 are directed to the production of durene and gasoline from syngas using a conventional methanol-to-gasoline process. Syngas is converted a mixture of durene and gasoline in two steps where the durene is separated from the gasoline by cooling and crystallization.
U.S. Pat. No. 4,444,652 is directed to the production and upgrading of low grade gasoline derived from syngas over an iron or cobalt catalyst. Low grade gasoline is upgraded with a C.sub.3 to C.sub.4 aliphatic hydrocarbon stream over a gallium-impregnated zeolite catalyst.
U.S. Pat. No. 4,399,234 is directed to production of gasoline via Fischer-Tropsch synthesis over cobalt/alumina catalysts.
U.S. Pat. No. 4,263,141 is directed to the production of gasoline from syngas using a conventional methanol-to-gasoline route in two stages. In the first stage syngas is converted to methanol over a copper based catalyst. Then the entire product stream is fed to a gasoline reactor the product of which is cooled and the C.sub.5 and higher gasoline fraction is collected as a product.
It is therefore an object of the present invention to provide a method for converting syngas, either hydrogen-rich or carbon monoxide-rich, to gasoline through an intermediate which comprises as a major portion dimethyl ether, which improves the reaction chemistry, productivity and heat transfer as compared to processes which utilize methanol as an intermediate.
It is a further object of the present invention to provide an improved process for converting syngas to gasoline whereby the lowering of the energy requirements is by about 15% or more as compared to a process utilizing methanol as an intermediate.
These and other objects will be apparent from the following description of the practice of the invention.